The invention relates to a control valve retaining element, which is used in a control valve of a brake booster and by means of which a bellows end and optionally an air filter element are accommodated and positioned relative to an actuating rod of the brake booster.
Such a control valve retaining element is used in particular for brake boosters, in which the boosting force results from an air pressure difference within the brake booster. Said brake boosters have, in a housing, two chambers which are separated from one another in a gastight manner by a movable wall. A control valve, which is usually actuable by means of an actuating rod, is used to feed into the one chamber selectively a pressure which is higher in comparison to the other chamber so as to produce at the movable wall a pressure difference, which gives rise to the desired boosting force. To protect the control valve from dust, dirt particles and other environmental influences it is surrounded by bellows, one end of which is fixed to the actuating rod by means of the said retaining element. Brake boosters of the described type mostly take the form of vacuum brake boosters. However, the invention may be used also for brake boosters which operate purely hydraulically.
From EP 0 790 910 B1 a retaining element is known, which is used to accommodate and position the end of a bellows, which protects the control valve of a vacuum brake booster from dirt, on an actuating rod of the control valve. The retaining element is disposed by means of a press fit immovably on the actuating rod and has at its pedal-side end a retaining collar, which accommodates the annular bellows end. Upon a displacement of the actuating rod the retaining element is entrained and, with it, the bellows end accommodated in the retaining collar.
As the retaining element is fastened by means of a press fit on the actuating rod, the manufacturing tolerances between the retaining element and the actuating rod have to be very exacting. This inevitably increases the cost of manufacturing the retaining element. The retaining element is moreover complex to install because it has to be pressed onto the actuating rod and at the same time an exact positioning of the retaining element relative to the actuating rod has to be effected. In the event of loosening of the press fit of the retaining element, the retaining element may shift out of the desired position relative to the actuating rod. The vacuum brake booster known from EP 0 790 910 B1 also has an annular cylindrical air filter element, which is disposed around the actuating rod and retained by a separate insert provided in the control valve housing.
A quite similar retaining element is known from DE 44 08 993 A1.
The object of the present invention is to provide a retaining element for accommodating and positioning a bellows end relative to an actuating rod in a vacuum brake booster, which retaining element is less expensive to manufacture and may be positioned easily and securely on the actuating rod.
The retaining element according to the invention should preferably also be able to accommodate and position an air filter element.
Like the known retaining element described initially, the control valve retaining element according to the invention for a brake booster comprises a hollow cylindrical base member and a first retaining collar, which is fitted on the base member and has at least one lateral wall for supporting a bellows end.
However, a second retaining collar is additionally provided, which projects radially inwards from a first end of the base member and extends in peripheral direction. The second retaining collar has a first lateral face, which is provided for cooperation with a step-shaped stop of a brake booster actuating rod, and an opposite second lateral face, which is provided for cooperation with a compression spring of the brake booster.
In said manner the control valve retaining element according to the invention may be fitted in a precisely defined position relative to the actuating rod by using a stop, which is already provided on the actuating rod and is acted upon in conventional brake boosters by a compression spring, which resets the actuating rod. The maintaining of said position is guaranteed by the clamping of the control valve retaining element between the compression spring and the stop of the actuating rod, i.e. the compression spring presses the second retaining collar towards the stop. In order further to simplify the manufacture and installation of the control valve retaining element according to the invention, the control valve retaining element according to the invention is preferably of an integral construction.
According to a preferred refinement of the retaining body according to the invention, its base member is provided with a third retaining body, which is used to accommodate an air filter.
By means of said third retaining collar, which preferably extends radially outwards from the base member and in peripheral direction, an e.g. annular air filter may be accommodated and positioned relative to the actuating rod. The number of elements to be assembled is therefore reduced, assembly is simplified and operational reliability increased.
In a further embodiment of the invention, the third retaining collar has an at least substantially S-shaped cross section.
In said manner a sufficiently wide supporting and/or retaining surface extending in peripheral direction is obtained for the air filter element. The third retaining collar is preferably provided at the first end of the base member.
According to a particularly preferred refinement of the control valve retaining element according to the invention, the second retaining collar defines an at least substantially annular opening, the diameter of which corresponds to an outside diameter of the actuating rod. The inside diameter of the base member is in said case preferably greater than the outside diameter of the actuating rod. Thus, during assembly of the brake booster the control valve retaining element according to the invention may easily be slipped onto the actuating rod until the first lateral face of the second retaining collar cooperates with the stop of the actuating rod. This eliminates the need for exact and elaborate positioning such as is necessary e.g. with use of a press fit.
The first retaining collar preferably also extends radially outwards from the base member. Furthermore, the first retaining collar is advantageously provided with two mutually spaced side walls extending parallel to one another for even more secure retention of the bellows end.
Although the control valve retaining element according to the invention may be made of any suitable material, for reasons of manufacture and cost it is preferably made of plastics material.